Chemical polishing (CP) methods and apparatus have been known for many years. Prior art CP apparatus are directed to polishing the surfaces of relatively tough semiconductor materials such as those composed of elemental silicon. On such common semiconductor (and insulator) materials, one can exert appreciable pressure on the face to be polished without causing failure of the workpiece.
Some semiconductor materials, particularly Group II-VI semiconductor materials and more particularly mercury cadmium telluride (MCT) and cadmium telluride (CT) materials, are more fragile and cannot withstand excessive downward pressure of the sort exerted in conventional polishing processes. By way of illustration, as measured on the Vickers scale, elemental silicon has a hardness of 1100 kg/mm2, GaSb a hardness of 450 kg/mm2, InSb a hardness of 438 kg/mm2, and Hg0.8Cd0.2Te a hardness of only 35 kg/mm2. Therefore, particularly for Group II-VI semiconductor materials, very low pressures must be used. To date, conventional CP apparatus have been less than satisfactory in using only light pressures yet exerting sufficient control.
Several conventional semiconductor polishing systems do not provide for the use of chemical polishing solutions. Exposed steel components and open air polishing systems prohibit the use of chemical etchants such as bromine and hydrochloric acid. The use of these chemicals is critical, however, for controlling the stoichiometry of the polished crystalline surface.